Reduction of coke formation during in situ combustion



United States Patent 3,363,686 REDUGTXON OF COKE FORMATION DURING INSHTU COMBUSTION Ralph Gilchrist, Bartlesville, Okla., assigpor toPhillips Petroleum Company, a corporation of Delaware No Drawing. FiledJan. 10, 1966, Ser. No. 519,452

9 Claims. (Cl. 166-11) This invention relates to an improved process forproducing oil from an oil-bearing stratum by in situ combustion.

The production of hydrocarbons from oil-bearing strata and othercarbonaceous deposits by in situ combustion is an accepted process inthe petroleum industry. In such a process, the carbonaceous material inthe stratum to be produced is ignited around a well penetrating thestratum and air or other O -containing, combustionsupporting gas is fedto the resulting combustion zone so as to move this zone thru thestratum toward one or more offset wells. In one method of operation, thecombustion-supporting gas is injected thru the ignition Well so as todrive the combustion zone to the offset well(s) concurrently to the flowof gas thru the stratum. In a stratum containing highly viscous oilwhich tends to congeal when warmed and driven into the cold stratum bydirect drive, reverse burning is usually resorted to. The reverseburning process involves igniting the stratum around a well in the usualmanner and injecting the combustion-supporting gas thru one or moreoffset wells so as to cause the combustion zone to move countercurrentlyto the flow of gas, the ignition well serving as a production well. Whenreverse burning is util1zed, a preferred procedure comprises injectingair thru the in ection well(s) until air appears in the ignition wellbefore initiating combustion around the ignition well.

Ignition is effected in any suitable manner, as by burning a charcoalpack, soaked with a heavy oil, in the ignition Well. Another method ofigniting the combustible material in the stratum comprises depositing aspontaneously-ignitable fuel such as tung oil or linseed oil in thestratum around the injection well and feeding air to the fuel area so asto ignite the same and initiate combustion of the in-place hydrocarbonmaterial. The spontaneouslyignitable fuel may be driven into the stratuma short distance, such as one to five feet, by injecting a fluid drivingagent after the injection of the fuel, in order to effect ignition aspaced distance from the ignition well, thereby protecting downholeequipment from the high-temperature combustion zone. These methods ofignition are disclosed and claimed in copending applications S.N. 520,-845, filed Jan. 17, 1966, and SN. 559,804, filed June 23, 1966.

In the production of hydrocarbons by in situ combustion, a portion ofthe carbonaceous deposit is burned and another portion is produced asfluidized and vaporized hydrocarbon material which appears in theproduction well(s) in admixture with the combustion gas produced by theburning. Another portion of the carbonaceous deposit is converted tocoke. In viscous oil deposits, the conversion to coke is particularlyexcessive unless measures are taken to reduce coke formation.

The instant invention is concerned with an improved in situ combustionprocess which substantially and materially minimizes coke formation in acarbonaceous deposit during in situ combustion.

Accordingly, it is an object of the invention to provide an improved insitu combustion process for the production of hydrocarbons from acarbonaceous deposit, which minimizes or materially reduces cokeformation. Another object is to provide a process which produces morehydrocarbon material from a carbonaceous deposit than is normallyproduced. Other objects of the invention will become apparent to oneskilled in the art upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises depositing in the carbonaceousstratum to be produced a liquid hydrocarbon fuel containing a ketal insufficient concentration to reduce the formation of coke during theburning of the in-place carbonaceous deposit with injected O -containinggas. The ketal has the formula RI wherein R is a C to C alkyl radical, Ris a C to C alkyl radical, and the total carbons is not greater than 20.

Ketals exemplary of those within the scope of the formula include2,2-dimethoxypropane, 6,6-di-n-but0xydodecane, 4,4-diisopropoxynonane,3,3-diethoxy-5-ethylheptane, and 2-ethoxy-Z-tertbutoxyhexane.

The ketals defined have the capacity to substantially and materiallyminimize coke formation during the combustion of the carbonaceousdeposit. Also, the burning of the injected fuel reduces the amount ofin-place carbonaceous material burned to maintain suitable combustionand production temperatures, thereby increasing the amount ofhydrocarbons produced by the combustion.

Various liquid hydrocarbon fuels may be utilized ranging from propanethru kerosene or even heavier fuels. LPG is an effective fuel sinceinjection pressures are suflicient to maintain this type of fuel inliquid form in the injection well and in the surrounding stratum. Theamount of fuel injected is in the range of 0.05 to 5 percent of the porevolume (based on the sweep pattern of the combustion Within the stratumto be produced). It is preferred to utilize the liquid fuel in an amountin the range of 0.1 to 3 percent of the pore volume. The ketal isincorporated in the liquidfuel in an amount in the range of 0.01 to 2.0volume percent; however, larger amounts may be utilized but the costinvolved when compared to the benefits derived therefrom is noteconomically justified.

It is feasible to inject the liquid fuel-ketal mixture into the stratumto be produced so as to admix the mixture with the in-place crude oilprior to the .initiation of combustion. In this manner, the auxiliaryfuel is burned in admixture with the ketal in the combustion zone as thecombustion zone is moved thru the stratum. Any method of depositing thefuel-ketal mixture in the stratum so that it is burned in the combustionzone is within the scope of the invention.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention I claim:

1. In a process for producing hydrocarbons from a combustiblecarbonaceous stratum by in situ combustion wherein an O -containing,combustion-supporting gas is fed into a combustion zone in said stratumthru an injection well therein to burn a portion of the carbonaceousmaterial with coke formation and produce a portion as hydrocarbons thruan offset production well in admixture with combustion gases, theimprovement comprising:

burning in said combustion zone an injected liquid hydrocarbon fuelcontaining a ketal having the formula wherein R is a C to C alkylradical, R is a C to C alkyl radical, and the total carbons is notgreater than 20, the concentration of said ketal in said liquid fuelbeing in the range of 0.01 to 2.0 volume percent and the resulting fuelmixture being in the range of 0.05 to 5 pore volume percent. 2. Theprocess of claim 1 Wherin said ketal comprises principally2,2-dimethoxypropane.

3. The process of claim 1 wherein said ketal comprises principally6,6-di-n-butoxydodecane.

4. The process of claim 1 wherein said ketal comprises principally4,4-diisopropoxynonane.

5. The process of claim 1 wherein said ketal comprises principally3,3-diethoxy-5-ethylheptane.

6. The process of claim 1 wherein said ketal comprises principally2-ethoxy-2-tertbutoxyhexane.

7. The process of claim 1 wherein said stratum contains a viscous crudeoil.

8. The process of claim 1 wherein said fuel is deposited in said stratumprior to initiation of combustion.

References Cited UNITED STATES PATENTS 2,382,471 8/1945 Frey 1661l2,722,277 11/1955 Crawford 16611 2,804,146 8/1957 Crawford 166-112,953,205 9/1960 Carr 166-11 3,007,520 11/1961 Frey 16611 3,127,9354/1957 Poettmann et al 16611 3,180,412 4/1965 Bednarski et al 16611OTHER REFERENCES Cram, D. I. and Hammond, G. 8.; Organic ChemistrySecond edition, McGraw-Hill Book Company, New York, N.Y., 1964 (pages295 to 297) QD 251 C7 1964 c. 3.

STEPHEN I. NOVOSAD, Primary Examiner.

1. IN A PROCESS FOR PRODUCING HYDROCARBONS FROM A COMBUSTIBLECARBONACEOUS STRATUM BY IN SITU COMBUSTION WHEREIN AN O2-CONTAINING,COMBUSTION-SUPPORTING GAS IS FED INTO A COMBUSTION ZONE IN SAID STRATUMTHRU AN INJECTION WELL THEREIN TO BURN A PORTION OF THE CARBONACEOUSMATERIAL WITH COKE FORMATION AND PRODUCE A PORTION AS HYDROCARBONS THRUAN OFFSET PRODUCTION WELL IN ADMIXTURE WITH COMBUSTION GASES, THEIMPROVEMENT COMPRISING: BURNING IN SAID COMBUSTION ZONE AN INJECTEDLIQUID HYDROCARBON FUEL CONTAINING A KETAL HAVING THE FORMULA